OVERPRESSURE ISOFLURANE AT CESAREAN-SECTION - A STUDY OF ARTERIAL ISOFLURANE CONCENTRATIONS

In this study we have measured arterial concentrations of isoflurane o btained during Caesarean section in two groups of patients. Patients i n group 1 received 1% isoflurane throughout operation, whilst those in group 2 received 2% isoflurane for the first 5 min, 1.5% for the next 5 min and 0.8% thereafter We found that arterial isoflurane concentra tions were significantly greater in group 2 than in group I (ANOVA, P < 0.05). Isoflurane concentrations greater than 30 mu g ml(-1) were ac hieved rapidly in most patients in both groups, but there was a large scatter of results. The isoflurane concentration at which awareness or recall may occur is not known, but an ''overpressure'' technique as d escribed for patients in group 2 may result in fewer patients being at risk of awareness.